Added PostConstruct Factory sample in Extras.

extras/pom.xml

@@ -40,9 +40,14 @@
     <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
-      <version>2.3.1</version>
+      <version>2.7</version>
       <scope>compile</scope>
     </dependency>
+    <dependency>
+      <groupId>javax.annotation</groupId>
+      <artifactId>jsr250-api</artifactId>
+      <version>1.0</version>
+    </dependency>
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
@@ -86,16 +91,16 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-compiler-plugin</artifactId>
-        <version>3.2</version>
+        <version>3.5.1</version>
         <configuration>
-          <source>1.5</source>
+          <source>1.6</source>
-          <target>1.5</target>
+          <target>1.6</target>
         </configuration>
       </plugin>
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-jar-plugin</artifactId>
-        <version>2.5</version>
+        <version>3.0.2</version>
         <executions>
           <execution>
             <phase>package</phase>
@@ -113,7 +118,7 @@
       <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-source-plugin</artifactId>
-         <version>2.4</version>
+         <version>3.0.1</version>
          <executions>
            <execution>
              <id>attach-sources</id>
@@ -127,7 +132,7 @@
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-javadoc-plugin</artifactId>
-         <version>2.10.1</version>
+         <version>2.10.4</version>
          <executions>
            <execution>
              <id>attach-javadocs</id>
@@ -147,7 +152,7 @@
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-eclipse-plugin</artifactId>
-         <version>2.9</version>
+         <version>2.10</version>
          <configuration>
            <downloadSources>true</downloadSources>
            <downloadJavadocs>true</downloadJavadocs>

extras/src/main/java/com/google/gson/typeadapters/PostConstructAdapterFactory.java

@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2016 Gson Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gson.typeadapters;
+
+import java.io.IOException;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+import javax.annotation.PostConstruct;
+
+import com.google.gson.Gson;
+import com.google.gson.TypeAdapter;
+import com.google.gson.TypeAdapterFactory;
+import com.google.gson.reflect.TypeToken;
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+
+public class PostConstructAdapterFactory implements TypeAdapterFactory {
+    // copied from https://gist.github.com/swankjesse/20df26adaf639ed7fd160f145a0b661a
+    @Override
+    public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
+        for (Class<?> t = type.getRawType(); t != Object.class; t = t.getSuperclass()) {
+            for (Method m : t.getDeclaredMethods()) {
+                if (m.isAnnotationPresent(PostConstruct.class)) {
+                    m.setAccessible(true);
+                    TypeAdapter<T> delegate = gson.getDelegateAdapter(this, type);
+                    return new PostConstructAdapter<T>(delegate, m);
+                }
+            }
+        }
+        return null;
+    }
+
+    final static class PostConstructAdapter<T> extends TypeAdapter<T> {
+        private final TypeAdapter<T> delegate;
+        private final Method method;
+
+        public PostConstructAdapter(TypeAdapter<T> delegate, Method method) {
+            this.delegate = delegate;
+            this.method = method;
+        }
+
+        @Override public T read(JsonReader in) throws IOException {
+            T result = delegate.read(in);
+            if (result != null) {
+                try {
+                    method.invoke(result);
+                } catch (IllegalAccessException e) {
+                    throw new AssertionError();
+                } catch (InvocationTargetException e) {
+                    if (e.getCause() instanceof RuntimeException) throw (RuntimeException) e.getCause();
+                    throw new RuntimeException(e.getCause());
+                }
+            }
+            return result;
+        }
+
+        @Override public void write(JsonWriter out, T value) throws IOException {
+            delegate.write(out, value);
+        }
+    }
+}

extras/src/test/java/com/google/gson/typeadapters/PostConstructAdapterFactoryTest.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2016 Gson Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.gson.typeadapters;
+
+import javax.annotation.PostConstruct;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
+import junit.framework.TestCase;
+
+public class PostConstructAdapterFactoryTest extends TestCase {
+    public void test() throws Exception {
+        Gson gson = new GsonBuilder()
+                .registerTypeAdapterFactory(new PostConstructAdapterFactory())
+                .create();
+        gson.fromJson("{\"bread\": \"white\", \"cheese\": \"cheddar\"}", Sandwich.class);
+        try {
+            gson.fromJson("{\"bread\": \"cheesey bread\", \"cheese\": \"swiss\"}", Sandwich.class);
+            fail();
+        } catch (IllegalArgumentException expected) {
+            assertEquals("too cheesey", expected.getMessage());
+        }
+    }
+
+    static class Sandwich {
+        String bread;
+        String cheese;
+
+        @PostConstruct void validate() {
+            if (bread.equals("cheesey bread") && cheese != null) {
+                throw new IllegalArgumentException("too cheesey");
+            }
+        }
+    }
+}